Nuclear Pore Proteins Research Articles

Selective degradation of multimeric proteins by TRIM21-based molecular glue and PROTAC degraders.

Targeted protein degradation (TPD) utilizes molecular glues or proteolysis-targeting chimeras (PROTACs) to eliminate disease-causing proteins by promoting their interaction with E3 ubiquitin ligases. Current TPD approaches are limited by reliance on a small number of constitutively active E3 ubiquitin ligases. Here, we report that (S)-ACE-OH, a metabolite of the antipsychotic drug acepromazine, acts as a molecular glue to induce an interaction between the E3 ubiquitin ligase TRIM21 and the nucleoporin NUP98, leading to the degradation of nuclear pore proteins and disruption of nucleocytoplasmic trafficking. Functionalization of acepromazine into PROTACs enabled selective degradation of multimeric proteins, such as those within biomolecular condensates, while sparing monomeric proteins. This selectivity is consistent with the requirement of substrate-induced clustering for TRIM21 activation. As aberrant protein assemblies cause diseases such as autoimmunity, neurodegeneration, and cancer, our findings highlight the potential of TRIM21-based multimer-selective degraders as a strategy to tackle the direct causes of these diseases.

Nup210 Promotes Colorectal Cancer Progression by Regulating Nuclear Plasma Transport

The nuclear pore complex (NPC) regulates nucleoplasmic transport, transcription, and genomic integrity in eukaryotic cells. However, little is known about how NPC works in cancer. In this study, we investigated the role of the nuclear pore protein 210 (Nucleoporin 210, Nup210) in colorectal cancer (CRC). Bioinformatics analysis revealed that the expression of Nup210 was increased in CRC and was associated with poor patient prognosis, but it was not a statistically significant independent prognostic factor. Moreover, knockdown of Nup210 in CRC cells inhibited the proliferation, invasion, and metastasis of CRC cells in vivo and in vitro. Additionally, nuclear size and nuclear plasma material transport capacity decreased along with the number and density of NPCs on the surface of CRC cells when Nup210 expression was inhibited. Furthermore, Nup210 required nuclear localization sequences (NLS) to localize to the nuclear membrane surface and interact with importin-α/β, which in turn affected the transit of nuclear plasma material. Importazole, a small molecule inhibitor of importin, along with therapy that targets the Nup210 protein is anticipated to be a novel strategy for CRC treatment. Their combination may be able to more effectively lower CRC tumor load. In conclusion, Nup210 modulates cellular nucleoplasmic transport capability and cell surface NPC density via NLS, thus promoting CRC progression. This discovery validates the molecular function of NPC in the development of CRC and provides a theoretical foundation for NPC-regulated nuclear import targeting as a therapeutic strategy for CRC.

Biology of Healthy Aging: Biological Hallmarks of Stress Resistance Related and Unrelated to Longevity in Humans

Stress resistance is highly associated with longer and healthier lifespans in various model organisms, including nematodes, fruit flies, and mice. However, we lack a complete understanding of stress resistance in humans; therefore, we investigated how stress resistance and longevity are interlinked in humans. Using more than 180 databases, we identified 541 human genes associated with stress resistance. The curated gene set is highly enriched with genes involved in the cellular response to stress. The Reactome analysis identified 398 biological pathways, narrowed down to 172 pathways using a medium threshold (p-value < 1 × 10−4). We further summarized these pathways into 14 pathway categories, e.g., cellular response to stimuli/stress, DNA repair, gene expression, and immune system. There were overlapping categories between stress resistance and longevity, including gene expression, signal transduction, immune system, and cellular responses to stimuli/stress. The categories include the PIP3-AKT-FOXO and mTOR pathways, known to specify lifespans in the model systems. They also include the accelerated aging syndrome genes (WRN and HGPS/LMNA), while the genes were also involved in non-overlapped categories. Notably, nuclear pore proteins are enriched among the stress-resistance pathways and overlap with diverse metabolic pathways. This study fills the knowledge gap in humans, suggesting that stress resistance is closely linked to longevity pathways but not entirely identical. While most longevity categories intersect with stress-resistance categories, some do not, particularly those related to cell proliferation and beta-cell development. We also note inconsistencies in pathway terminologies with aging hallmarks reported previously, and propose them to be more unified and integral.

The nuclear pore protein Nup2 is essential for growth and development, stress response, pathogenicity and deoxynivalenol biosynthesis in Fusarium graminearum.

Wheat is an important grain crop that has been under serious threat from Fusarium graminearum. Nup2, a member of the nuclear pore complex, plays an important role in regulating eukaryotic nuclear protein transport and participates in gene regulation. Dissecting the function of nuclear pore proteins in pathogenic fungi may provide effective targets for novel fungicides. Mutants exhibited nutritional growth defects, asexual/sexual developmental abnormalities. Deficiency of FgNup2 resulted in increased resistance of Fusarium graminearum to cell wall disruptors and increased sensitivity to metal ions. Pathogenicity analyses showed that the mutant was significantly less virulent on flowering wheat ears, consistent with the observed decrease in deoxynivalenol (DON) production. Furthermore, we showed that FgNup2 interacts synergistically with FgTri6, a transcription factor of the TRI family, to regulate the expression of toxin-producing genes, which, in turn, affects the biosynthesis of DON and related toxins. This study revealed that FgNup2 plays important roles in the growth and development, cell wall integrity, stress response, pathogenicity, and DON synthesis of F. graminearum. © 2024 Society of Chemical Industry.

Rapid evolution of promoters from germline-specifically expressed genes including transposon silencing factors

BackgroundThe piRNA pathway in animal gonads functions as an ‘RNA-based immune system’, serving to silence transposable elements and prevent inheritance of novel invaders. In Drosophila, this pathway relies on three gonad-specific Argonaute proteins (Argonaute-3, Aubergine and Piwi) that associate with 23–28 nucleotide piRNAs, directing the silencing of transposon-derived transcripts. Transposons constitute a primary driver of genome evolution, yet the evolution of piRNA pathway factors has not received in-depth exploration. Specifically, channel nuclear pore proteins, which impact piRNA processing, exhibit regions of rapid evolution in their promoters. Consequently, the question arises whether such a mode of evolution is a general feature of transposon silencing pathways.ResultsBy employing genomic analysis of coding and promoter regions within genes that function in transposon silencing in Drosophila, we demonstrate that the promoters of germ cell-specific piRNA factors are undergoing rapid evolution. Our findings indicate that rapid promoter evolution is a common trait among piRNA factors engaged in germline silencing across insect species, potentially contributing to gene expression divergence in closely related taxa. Furthermore, we observe that the promoters of genes exclusively expressed in germ cells generally exhibit rapid evolution, with some divergence in gene expression.ConclusionOur results suggest that increased germline promoter evolution, in partnership with other factors, could contribute to transposon silencing and evolution of species through differential expression of genes driven by invading transposons.

The nuclear pore protein NUP98 impedes LTR-driven basal gene expression of HIV-1, viral propagation, and infectivity.

Nucleoporins (NUPs) are cellular effectors of human immunodeficiency virus-1 (HIV-1) replication that support nucleocytoplasmic trafficking of viral components. However, these also non-canonically function as positive effectors, promoting proviral DNA integration into the host genome and viral gene transcription, or as negative effectors by associating with HIV-1 restriction factors, such as MX2, inhibiting the replication of HIV-1. Here, we investigated the regulatory role of NUP98 on HIV-1 as we observed a lowering of its endogenous levels upon HIV-1 infection in CD4+ T cells. Using complementary experiments in NUP98 overexpression and knockdown backgrounds, we deciphered that NUP98 negatively affected HIV-1 long terminal repeat (LTR) promoter activity and lowered released virus levels. The negative effect on promoter activity was independent of HIV-1 Tat, suggesting that NUP98 prevents the basal viral gene expression. ChIP-qPCR showed NUP98 to be associated with HIV-1 LTR, with the negative regulatory element (NRE) of HIV-1 LTR playing a dominant role in NUP98-mediated lowering of viral gene transcription. Truncated mutants of NUP98 showed that the attenuation of HIV-1 LTR-driven transcription is primarily contributed by its N-terminal region. Interestingly, the virus generated from the producer cells transiently expressing NUP98 showed lower infectivity, while the virus generated from NUP98 knockdown CD4+ T cells showed higher infectivity as assayed in TZM-bl cells, corroborating the anti-HIV-1 properties of NUP98. Collectively, we show a new non-canonical function of a nucleoporin adding to the list of moonlighting host factors regulating viral infections. Downregulation of NUP98 in a host cell upon HIV-1 infection supports the concept of evolutionary conflicts between viruses and host antiviral factors.

Murine leukemia virus infection of non-dividing dendritic cells is dependent on nucleoporins.

Retroviral reverse transcription starts within the capsid and uncoating and reverse transcription are mutually dependent. There is still debate regarding the timing and cellular location of HIV's uncoating and reverse transcription and whether it occurs solely in the cytoplasm, nucleus or both. HIV can infect non-dividing cells because there is active transport of the preintegration complex (PIC) across the nuclear membrane, but Murine Leukemia Virus (MLV) is thought to depend on cell division for replication and whether MLV uncoating and reverse transcription is solely cytoplasmic has not been studied. Here, we used NIH3T3 and primary mouse dendritic cells to determine where the different stages of reverse transcription occur and whether cell division is needed for nuclear entry. Our data strongly suggest that in both NIH3T3 cells and dendritic cells (DCs), the initial step of reverse transcription occurs in the cytoplasm. However, we detected MLV RNA/DNA hybrid intermediates in the nucleus of dividing NIH3T3 cells and non-dividing DCs, suggesting that reverse transcription can continue after nuclear entry. We also confirmed that the MLV PIC requires cell division to enter the nucleus of NIH3T3 cells. In contrast, we show that MLV can infect non-dividing primary DCs, although integration of MLV DNA in DCs still required the viral p12 protein. Knockdown of several nuclear pore proteins dramatically reduced the appearance of integrated MLV DNA in DCs but not NIH3T3 cells. Additionally, MLV capsid associated with the nuclear pore proteins NUP358 and NUP62 during infection. These findings suggest that simple retroviruses, like the complex retrovirus HIV, gain nuclear entry by traversing the nuclear pore complex in non-mitotic cells.

Nuclear pore protein POM121 regulates subcellular localization and transcriptional activity of PPARγ

Manipulation of the subcellular localization of transcription factors by preventing their shuttling via the nuclear pore complex (NPC) emerges as a novel therapeutic strategy against cancer. One transmembrane component of the NPC is POM121, encoded by a tandem gene locus POM121A/C on chromosome 7. Overexpression of POM121 is associated with metabolic diseases (e.g., diabetes) and unfavorable clinical outcome in patients with colorectal cancer (CRC). Peroxisome proliferator-activated receptor-gamma (PPARγ) is a transcription factor with anti-diabetic and anti-tumoral efficacy. It is inhibited by export from the nucleus to the cytosol via the RAS-RAF-MEK1/2-ERK1/2 signaling pathway, a major oncogenic driver of CRC. We therefore hypothesized that POM121 participates in the transport of PPARγ across the NPC to regulate its transcriptional activity on genes involved in metabolic and tumor control. We found that POM121A/C mRNA was enriched and POM121 protein co-expressed with PPARγ in tissues from CRC patients conferring poor prognosis. Its interactome was predicted to include proteins responsible for tumor metabolism and immunity, and in-silico modeling provided insights into potential 3D structures of POM121. A peptide region downstream of the nuclear localization sequence (NLS) of POM121 was identified as a cytoplasmic interactor of PPARγ. POM121 positivity correlated with the cytoplasmic localization of PPARγ in patients with KRAS mutant CRC. In contrast, POM121A/C silencing by CRISPR/Cas9 sgRNA or siRNA enforced nuclear accumulation of PPARγ and activated PPARγ target genes promoting lipid metabolism and cell cycle arrest resulting in reduced proliferation of human CRC cells. Our data suggest the POM121-PPARγ axis as a potential drugable target in CRC.

The Role of Nucleoporins in Cardiac Tissue Development and Disease.

Nuclear pore complexes (NPCs) are intricate intracellular structures composed of approximately 30 nuclear pore proteins (NUPs) that regulate the transport of materials between the nucleus and cytoplasm in eukaryotic cells. The heart is a crucial organ for sustaining the vital functions of the body, pumping blood rich in nutrients and energy to all organs and tissues. Recent studies have shown that NPCs play pivotal roles not only in normal cardiac physiological processes such as myocardial cell proliferation and differentiation but also in various pathological processes such as ischemic and hypoxic myocardial injury. Due to their mass and complicated nature, the structures of NPCs have been challenging to identify by the scientific community. With the development of cryo-electron microscopy and advanced sampling techniques, researchers have made significant progress in understanding the structures of NPCs. This review aims to summarize the latest research on the structural aspects of NPCs and their roles in cardiac physiology and pathology, increase the understanding of the intricate mechanisms of NPC actions, provide valuable insights into the pathogenesis of heart diseases and describe the development of potential novel therapeutic strategies.

SYSTEMS BIOLOGY OF HUMAN AGING - NETWORK MODEL 2023

Abstract This network is presented to aid in conceptualizing the many processes of aging, the causal chains of events, the interactions among them, feedback, and vicious cycles. It suggests promising intervention points for therapy development. The signs of human senescence are hypothesized to result from several primary causes. This network includes both intracellular and extracellular processes, ranging from molecular to whole-body. Lifestyle, environment, and proposed interventions are highlighted. Important pathways include: Nuclear mutations, transposon insertions, telomere shortening, chromosome breaks, chromatin alterations, epigenetic DNA adducts. Extracellular protein damage results in stiffness, weakness, inflammation. Altered niches for cells cause transdifferentiation, arrested cell division, cell death, cancer, stem cell depletion, tissue wasting, neurodegeneration, organ malfunction. Stiffer blood vessels promote stroke, heart disease. Lysosomes accumulate reactive, crosslinked Lipofuscin, which impairs autophagic turnover of macromolecules and organelles. Lipofuscin leaking into cytosol triggers apoptosis. Mitochondrial DNA Mutates; Lamin-A progerin, accumulates in nuclear scaffold, impairing mitosis and telomere maintenance. Nuclear Envelope Pore Proteins become oxidized, allowing inappropriate traffic of other proteins into and out of nucleus. Oxidized Aggregates in cytoplasm crosslink, resist turnover, inhibit proteasome activity, increase redox poise, and physically interfere with intracellular transport in axons. Proteasomes inhibited, reduce turnover of damaged molecules and expired molecular signals. Increased Redox Poise alters signaling and enzyme activities, and erodes telomeres. Inflammatory Cascades, promoted by damaged molecules and sick cells, further damage tissues. Neuroendocrine and immune systems degrade. Misfolded Proteins accumulate in Endoplasmic Reticulum. This diagram is maintained on the Web as a reference for researchers and students. www.LegendaryPharma.com/chartbg.html

Non-classical functions of nuclear pore proteins in ciliopathy.

Nucleoporins (NUPs) constitute integral nuclear pore protein (NPC) elements. Although traditional NUP functions have been extensively researched, evidence of additional vital non-NPC roles, referred to herein as non-classical NUP functions, is also emerging. Several NUPs localise at the ciliary base. Indeed, Nup188, Nup93 or Nup205 knockdown results in cilia loss, impacting cardiac left-right patterning in models and cell lines. Genetic variants of Nup205 and Nup188 have been identified in patients with congenital heart disease and situs inversus totalis or heterotaxy, a prevalent human ciliopathy. These findings link non-classical NUP functions to human diseases. This mini-review summarises pivotal NUP interactions with NIMA-related kinases or nephronophthisis proteins that regulate ciliary function and explores other NUPs potentially implicated in cilia-related disorders. Overall, elucidating the non-classical roles of NUPs will enhance comprehension of ciliopathy aetiology.

The role of the FSGS disease gene product and nuclear pore protein NUP205 in regulating nuclear localization and activity of transcriptional regulators YAP and TAZ.

Mutations in genes encoding nuclear pore proteins (NUPs) lead to the development of steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis (FSGS). However, the precise molecular mechanisms by which NUP dysfunction contributes to podocyte injury preceding FSGS remain unclear. The tightly regulated activity of Yes-associated protein (YAP) and WW-domain-containing transcription regulator 1 (TAZ), the transcriptional effectors of the Hippo pathway, is crucial for podocytes and the maintenance of the glomerular filter. In this study, we investigate the impact of NUPs on the regulation of YAP/TAZ nuclear import and activity in podocytes. In unbiased interactome studies using quantitative label-free mass spectrometry, we identify the FSGS disease gene products NUP107, NUP133, NUP205, and Exportin-5 (XPO5) as components of YAP and TAZ protein complexes in podocytes. Moreover, we demonstrate that NUP205 is essential for YAP/TAZ nuclear import. Consistently, both the nuclear interaction of YAP/TAZ with TEA domain transcription factor 1 and their transcriptional activity were dependent on NUP205 expression. Additionally, we elucidate a regulatory feedback mechanism whereby YAP activity is modulated in response to TAZ-mediated NUP205 expression. In conclusion, this study establishes a connection between the FSGS disease protein NUP205 and the activity of the transcriptional regulators and Hippo effectors YAP and TAZ and it proposes a potential pathological role of YAP/TAZ dysregulation in podocytes of patients with pathogenic NUP205 variants.

Nuclear elongation during spermiogenesis depends on physical linkage of nuclear pore complexes to bundled microtubules by Drosophila Mst27D.

Spermatozoa in animal species are usually highly elongated cells with a long motile tail attached to a head that contains the haploid genome in a compact and often elongated nucleus. In Drosophila melanogaster, the nucleus is compacted two hundred-fold in volume during spermiogenesis and re-modeled into a needle that is thirty-fold longer than its diameter. Nuclear elongation is preceded by a striking relocalization of nuclear pore complexes (NPCs). While NPCs are initially located throughout the nuclear envelope (NE) around the spherical nucleus of early round spermatids, they are later confined to one hemisphere. In the cytoplasm adjacent to this NPC-containing NE, the so-called dense complex with a strong bundle of microtubules is assembled. While this conspicuous proximity argued for functional significance of NPC-NE and microtubule bundle, experimental confirmation of their contributions to nuclear elongation has not yet been reported. Our functional characterization of the spermatid specific Mst27D protein now resolves this deficit. We demonstrate that Mst27D establishes physical linkage between NPC-NE and dense complex. The C-terminal region of Mst27D binds to the nuclear pore protein Nup358. The N-terminal CH domain of Mst27D, which is similar to that of EB1 family proteins, binds to microtubules. At high expression levels, Mst27D promotes bundling of microtubules in cultured cells. Microscopic analyses indicated co-localization of Mst27D with Nup358 and with the microtubule bundles of the dense complex. Time-lapse imaging revealed that nuclear elongation is accompanied by a progressive bundling of microtubules into a single elongated bundle. In Mst27D null mutants, this bundling process does not occur and nuclear elongation is abnormal. Thus, we propose that Mst27D permits normal nuclear elongation by promoting the attachment of the NPC-NE to the microtubules of the dense complex, as well as the progressive bundling of these microtubules.

ADAD1 is required for normal translation of nuclear pore and transport protein transcripts in spermatids of Mus musculus†.

ADAD1 is a testis-specific RNA-binding protein expressed in post-meiotic spermatids whose loss leads to defective sperm and male infertility. However, the drivers of the Adad1 phenotype remain unclear. Morphological and functional analysis of Adad1 mutant sperm showed defective DNA compaction, abnormal head shaping, and reduced motility. Mutant testes demonstrated minimal transcriptome changes; however, ribosome association of many transcripts was reduced, suggesting ADAD1 may be required for their translational activation. Further, immunofluorescence of proteins encoded by select transcripts showed delayed protein accumulation. Additional analyses demonstrated impaired subcellular localization of multiple proteins, suggesting protein transport is also abnormal in Adad1 mutants. To clarify the mechanism giving rise to this, the manchette, a protein transport microtubule network, and the LINC (linker of nucleoskeleton and cytoskeleton) complex, which connects the manchette to the nuclear lamin, were assessed across spermatid development. Proteins of both displayed delayed translation and/or localization in mutant spermatids implicating ADAD1 in their regulation, even in the absence of altered ribosome association. Finally, ADAD1's impact on the NPC (nuclear pore complex), a regulator of both the manchette and the LINC complex, was examined. Reduced ribosome association of NPC encoding transcripts and reduced NPC protein abundance along with abnormal localization in Adad1 mutants confirmed ADAD1's impact on translation is required for a NPC in post-meiotic germ cells. Together, these studies lead to a model whereby ADAD1's influence on nuclear transport leads to deregulation of the LINC complex and the manchette, ultimately generating the range of physiological defects observed in the Adad1 phenotype.

Indel driven rapid evolution of core nuclear pore protein gene promoters

Nuclear pore proteins (Nups) prominently are among the few genes linked to speciation from hybrid incompatibility in Drosophila. These studies have focused on coding sequence evolution of Nup96 and Nup160 and shown evidence of positive selection driving nucleoporin evolution. Intriguingly, channel Nup54 functionality is required for neuronal wiring underlying the female post-mating response induced by male-derived sex-peptide. A region of rapid evolution in the core promoter of Nup54 suggests a critical role for general transcriptional regulatory elements at the onset of speciation, but whether this is a general feature of Nup genes has not been determined. Consistent with findings for Nup54, additional channel Nup58 and Nup62 promoters also rapidly accumulate insertions/deletions (indels). Comprehensive examination of Nup upstream regions reveals that core Nup complex gene promoters accumulate indels rapidly. Since changes in promoters can drive changes in expression, these results indicate an evolutionary mechanism driven by indel accumulation in core Nup promoters. Compensation of such gene expression changes could lead to altered neuronal wiring, rapid fixation of traits caused by promoter changes and subsequently the rise of new species. Hence, the nuclear pore complex may act as a nexus for species-specific changes via nucleo-cytoplasmic transport regulated gene expression.

Characterisation of the trans-membrane nucleoporins GP210 and NDC1 in Arabidopsis thaliana

The nuclear pore is structurally conserved across eukaryotes as are many of the pore's constituent proteins. The transmembrane nuclear pore proteins GP210 and NDC1 span the nuclear envelope holding the nuclear pore in place. Orthologues of GP210 and NDC1 in Arabidopsis were investigated through characterisation of T-DNA insertional mutants. While the T-DNA insert into GP210 reduced expression of the gene, the insert in the NDC1 gene resulted in increased expression in both the ndc1 mutant as well as the ndc1/gp210 double mutant. The ndc1 and gp210 individual mutants showed little phenotypic difference from wild-type plants, but the ndc1/gp210 mutant showed a range of phenotypic effects. As with many plant nuclear pore protein mutants, these effects included non-nuclear phenotypes such as reduced pollen viability, reduced growth and glabrous leaves in mature plants. Importantly, however, ndc1/gp210 exhibited nuclear-specific effects including modifications to nuclear shape in different cell types. We also observed functional changes to nuclear transport in ndc1/gp210 plants, with low levels of cytoplasmic fluorescence observed in cells expressing nuclear-targeted GFP. The lack of phenotypes in individual insertional lines, and the relatively mild phenotype suggests that additional transmembrane nucleoporins, such as the recently-discovered CPR5, likely compensate for their loss.

Expression of nuclear pore protein POM121 in childhood acute lymphoblastic leukemias and its relationship with prognosis

Purpose: We aimed to investigate the status of POM121 gene expression, which is one of the nuclear pore proteins in childhood acute lymphoblastic leukemias (ALL), compared with the normal population, and its relationship with prognosis and other clinical findings.
 Materials and Methods: Fifty-nine patients with ALL followed up and treated between January 2008 and November 2013, and 36 control subjects were included in the study. A real-time PCR method was used to detect POM121 gene expressions.
 Results: The mean value of POM121 expression was 3.75±2.91 in ALL patients and 3.32±3.76 in the control group. The 3 and 10 year overall survival (OS) was better in ALL with lower POM121 expression (77%, 70% versus 68%, 58%, respectively). Although the OS was better in B-ALL patients, with lower POM121 expression (84%, 75% versus 54%, 46%, respectively), in T-ALL, in contrast, the OS results were better in patients with a higher POM121 expression (90%, 90% versus 60%, 60%, respectively). Patients with a higher POM121 expression than the mean of the control group and who had relapse and central nervous system involvement had statistically significantly lower OS results in the 3rd and 10th years (16%, 0% versus 84%, 78%, respectively).
 Conclusion: High POM121 expression negatively affects the prognosis in patients with ALL. This is a study to show the relationship between POM121 expression and prognosis in childhood acute lymphoblastic leukemias, POM121 function will be clarified further with more comprehensive studies.

Identification of Target Proteins for Promoting Nuclear Envelope Rupture in Cancer Cells

The nuclear envelope separates and protects DNA from the cytoplasm. In cancer cells, frequent nuclear morphological abnormalities and transient rupture of the nuclear membrane promote DNA damage and cancer malignancy. However, nuclear envelope instability, acting as a tumor-promotion factor, can be viewed as a fatal weakness of cancer cells. Although the exact mechanism is not clear, it is known that the loss of the tumor suppressor gene TP53 is involved in nuclear envelope instability in cancer cells. In this study, we demonstrate that the inhibition of NUP93, which is a subunit of the nuclear pore complex, induces cell death by enhancing nuclear envelope instability. The RNA interference (RNAi) inhibiting NUP93 expression in the human cell line RPE1 caused nuclear envelope rupture, and DNA damage, leading to cell death. Under the condition in which the tumor suppressor gene TP53 was simultaneously suppressed with NUP93, nuclear envelope rupture and DNA damage were significantly increased. Conversely, cell death was slightly decreased. The decrease in cell death may be ascribed to the fact that TP53 is involved in the induction of apoptosis by DNA damage. We speculate that amplification of nuclear envelope instability may induce cancer cell-specific synthetic lethality in the context of TP53-independent nuclear envelope instability. Moreover, our results suggest that nuclear pore proteins can be promising targets for the development of synthetic lethal anticancer drugs.

The role of O-GlcNAcylation in mRNA nuclear export studied by single-molecule super-resolution microscopy.

Characterizing the relationship between the nuclear export of mRNA and the O-GlcNAcylation of nuclear pore proteins is a critical process for understanding the dynamic effects of post-translational modifications on membrane protein structures. Specifically, it was reported that the concentration of O-GlcNAcylated nucleoporins (Nups) in the nuclear pore complexes (NPCs) can be significantly altered by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) inhibitor drugs. Combining two single-molecule super-resolution microscopy methods, STORM and SPEED microscopy, we found that the amount of messenger ribonucleoprotein particles (mRNPs) that successfully export through the NPC is approximately doubled when increasing the O-GlcNAcylation in the NPC. Reversely, five-fold less mRNPs can exit the nucleus to reach the cytoplasm with the decreased O-GlcNAcylation of Nups. Moreover, a virtual 3D imaging by SPEED microscopy revealed that the spatial distributions of these altered O-GlcNAcylated Nups colocalized well with the locations of Nups that are rich in phenylalanine-glycine (FG) repeats, suggesting the passage of mRNPs through the selective permeability barrier in the NPC is regulated by the amount of O-GlcNAcylated FG-Nups.

Licensing instead of fueling: Glutamine synthetase promotes mitotic progression via a non-metabolic mechanism

A recent report published in Nature Metabolism identified that glutamine synthetase (GS), the only enzyme in mammals to produce glutamine from glutamate, can directly control cancer cell mitosis by governing the APC/C complex via a metabolism-independent mechanism. It reported that GS can directly interact with the nuclear pore protein NUP88 to abolish its binging with CDC20, therefore licensing the activation of APC/CCDC20 to permit proper metaphase to anaphase transition of mitosis. These findings illustrated a dual-function mode of action of GS in cancer cells, in which GS’s metabolic and non-metabolic functions coordinate with the concentration change of glutamine in the tumor microenvironment (TME) to ensure cell survival or proliferation, respectively. These findings revealed the multi-faceted roles of glutamine synthetase in tumor development and underscored the potential to target non-canonical functions of glutamine synthetase for cancer treatment.